Image encoding/decoding method and device

ABSTRACT

Disclosed are an image encoding/decoding method and device supporting a plurality of layers. The image decoding method supporting the plurality of layers comprises the steps of; receiving a bitstream comprising the plurality of layers; and decoding the bitstream so as to acquire maximum number information about sublayers with respect to each of the plurality of layers.

TECHNICAL FIELD

The present invention relates to picture encoding and decoding, and moreparticularly, to picture encoding and decoding based on scalable videocoding (SVC).

BACKGROUND ART

In recent years, while a multimedia environment has been built up,various terminals and networks have been used and the resulting userequirement has been diversified.

For example, as a performance and a computing capability of a terminalhave been diversified, a supported performance has also been diversifiedfor each apparatus. Further, in the case of a network in whichinformation is transmitted, a pattern, an information amount, and atransmission speed of the transmitted information, as well as anexternal structure such as wired and wireless networks have beendiversified for each function. A user has selected a terminal and anetwork to be used according to a desired function and further,spectrums of a terminal and a network which an enterprise provides tothe user have been diversified.

In this regard, in recent years, as a broadcast having a high definition(HD) resolution has been extended and serviced worldwide as well asdomestically, a lot of users have been familiar with a high definitionpicture. As a result, a lot of picture service associated organizationshave made a lot of efforts to develop a next-generation pictureapparatus.

Further, with an increase in interest in ultra high definition (UHD)having four times higher resolution than an HDTV as well as the HDTV, arequirement for technology that compresses and processes a higherresolution and higher definition picture has been further increased.

In order to compress and process the picture, inter predictiontechnology of predicting a pixel value included in a current picturefrom a temporally prior and/or post picture, intra prediction technologyof predicting another pixel value included in the current picture byusing pixel information in the current picture, and entropy encodingtechnology of allocating a short sign to a symbol in which an appearancefrequency is high and a long sign to a symbol in which the appearancefrequency is low, and the like may be used.

As described above, when respective terminals and networks havingdifferent supported functions, and the diversified user requirements areconsidered, a quality, a size, a frame, and the like of a supportedpicture need to be consequently diversified.

As such, due to heterogeneous communication networks, and terminalshaving various functions and various types of terminals, scalabilitythat variously supports the quality, resolution, size, frame rate, andthe like of the picture becomes a primary function of a video format.

Accordingly, it is necessary to provide a scalability function so as toachieve video encoding and decoding in terms of temporal, spatial,picture quality, and the like in order to provide a service required bythe user under various environments based on a high-efficiency videoencoding method.

DISCLOSURE Technical Problem

An object of the present invention is to provide a method and anapparatus for picture encoding/decoding that can improveencoding/decoding efficiency.

Another object of the present invention is to provide a method and anapparatus that perform inter-layer switching in scalable video codingthat can improve encoding/decoding efficiency.

Yet another object of the present invention is to provide a method andan apparatus that express and signal scalability information of ascalable bitstream that can improve encoding/decoding efficiency.

Still another object of the present invention is to provide a method andan apparatus that express and signal sub-layer information of a scalablelayer that can improve encoding/decoding efficiency.

Technical Solution

In accordance with an aspect of the present invention, there is provideda method for picture decoding supporting a plurality of layers. Themethod for picture decoding supporting the plurality of layers includes:receiving a bitstream including the plurality of layers; and acquiringinformation on the maximum number of sub-layers for each of theplurality of layers by decoding the bitstream.

In accordance with another aspect of the present invention, there isprovided a method for picture encoding supporting a plurality of layers.The method for picture encoding supporting a plurality of layersincludes: acquiring information on the maximum number of sub-layers foreach of the plurality of layers; and transmitting a bitstream includingthe information on the maximum number of sub-layers by encoding theinformation on the maximum number of sub-layers.

In accordance with yet another aspect of the present invention, there isprovided an apparatus for picture decoding supporting a plurality oflayers. The apparatus for picture decoding supporting the plurality oflayers includes: a decoding unit receiving a bitstream including theplurality of layers and decoding the bitstream to acquire information onthe maximum number of sub-layers for each of the plurality of layers.

In accordance with still another aspect of the present invention, thereis provided an apparatus for picture encoding supporting a plurality oflayers. The apparatus for picture encoding supporting a plurality oflayers includes: an encoding unit deciding information on the maximumnumber of sub-layers for each of the plurality of layers and encodingthe information on the maximum number of sub-layers to transmit abitstream including the information on the maximum number of sub-layers.

Advantageous Effects

A method of describing extraction in a hierarchical bitstream andscalability information is provided to flexibly express various types ofscalability information of a bitstream and enable efficient adaptivetransformation at a packet level.

Further, various scalability information of a bitstream encoded by usinghierarchical picture encoding is efficiently expressed to allow abitstream extractor to easily extract a desired layer.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration of a picturedecoding apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a picturedecoding apparatus according to an embodiment of the present invention.

FIG. 3 is a conceptual diagram schematically illustrating one example ofa scalable video coding structure using a plurality of layers accordingto the present invention.

FIG. 4 is a flowchart schematically illustrating a method for pictureencoding, which supports a scalable bitstream (hierarchical bitstream)according to an embodiment of the present invention.

FIG. 5 is a flowchart schematically illustrating a method for picturedecoding, which supports a scalable bitstream (hierarchical bitstream)according to an embodiment of the present invention.

FIG. 6 is a flowchart schematically illustrating a method for signalsub-layer information for a scalable layer in a pictureencoding/decoding structure, which supports a scalable bitstream(hierarchical bitstream) according to an embodiment of the presentinvention.

MODE FOR INVENTION

Hereinafter, embodiments of the present invention will be described indetail with reference to the accompanying drawings. In describing theembodiments of the present specification, when it is determined that thedetailed description of the known art related to the present inventionmay obscure the gist of the present invention, the correspondingdescription thereof may be omitted.

It will be understood that when an element is simply referred to asbeing ‘connected to’ or ‘coupled to’ another element without being‘directly connected to’ or ‘directly coupled to’ another element in thepresent description, it may be ‘directly connected to’ or ‘directlycoupled to’ another element or be connected to or coupled to anotherelement, having the other element intervening therebetween. Moreover, acontent of describing “including” a specific component in thespecification does not exclude a component other than the correspondingcomponent and means that an additional component may be included in theembodiments of the present invention or the scope of the technicalspirit of the present invention.

Terms such first, second, and the like may be used to describe variouscomponents, but the components are not limited by the terms. The aboveterms are used only to discriminate one component from the othercomponent. For example, without departing from the scope of the presentinvention, a first component may be referred to as a second component,and similarly, a second component may be referred to as a firstcomponent.

Further, components described in the embodiments of the presentinvention are independently illustrated in order to show differentcharacteristic functions and each component is not constituted byseparated hardware or one software constituting unit. That is, eachcomponent includes respective components which are arranged for easydescription and at least two components of the respective components mayconstitute one component or one component is divided into a plurality ofcomponents which may perform their functions. Even an integratedembodiment and separated embodiments of each component is also includedin the scope of the present invention without departing from the spiritof the present invention.

Further, some components are not requisite components that performessential functions but selective components for just improvingperformance in the present invention. The present invention may beimplemented with the requisite component for implementing the spirit ofthe present invention other than the component used to just improve theperformance and a structure including only the requisite component otherthan the selective component used to just improve the performance isalso included in the scope of the present invention.

FIG. 1 is a block diagram illustrating a configuration of a picturedecoding apparatus according to an embodiment of the present invention.

A method or an apparatus for scalable video encoding/decoding may beimplemented by extension of a general picture encoding/decoding methodor apparatus which does not provide scalability and the block diagram ofFIG. 1 illustrates an embodiment of a picture encoding apparatus whichmay be a base of the scalable video encoding apparatus.

Referring to FIG. 1, a picture encoding apparatus 100 includes a motionestimation module 111, a motion compensation module 112, an intraprediction module 120, a switch 115, a subtractor 125, a transformmodule 130, a quantization module 140, an entropy encoding module 150, adequantization module 160, an inverse transform module 170, an adder175, a filter module 180, and a decoded picture buffer 190.

The picture encoding apparatus 100 may encode an input picture in anintra mode or an inter mode and output a bitstream. In the intra mode,the switch 115 may be switched to intra and in the inter mode, theswitch 115 may be switched to inter. The intra prediction means anintra-frame prediction and the inter prediction means an inter-frameprediction. The picture encoding apparatus 100 may generate a predictedblock for an input block of the input picture and thereafter, encode aresidual between the input block and the predicted block. In this case,the input picture may mean an original picture.

In the intra mode, the intra prediction module 120 may generate thepredicted block by performing a spatial prediction by using a pixelvalue of an already encoded/decoded block adjacent to a current block.

In the inter mode, the motion estimation module 111 may acquire a motionvector by finding an area of a reference picture stored in the decodedpicture buffer 190 which most matches the input block during a motionestimation process. The motion compensation module 112 compensates for amotion by using the motion vector to generate the predicted block.Herein, the motion vector is a 2D vector used in the inter predictionand may represent an offset between a current encoding/decoding targetpicture and a reference picture.

The subtractor 125 may generate a residual block by difference betweenthe input block and the generated predicted block.

The transform module 130 performs transformation for the residual blockto output a transform coefficient. Herein, the transform coefficient maymean a coefficient value generated by converting the residual blockand/or a residual signal. Hereinafter, in this specification, thetransform coefficient is quantized and a quantized transform coefficientlevel may also be called the transform coefficient.

The quantization module 140 quantizes an input transform coefficientaccording to a quantization parameter to output a quantized coefficient.The quantized coefficient may be called the quantized transformcoefficient level. In this case, the quantization module 140 mayquantize the input transform coefficient by using a quantization matrix.

The entropy encoding module 150 performs entropy encoding based onvalues calculated by the quantization module 140 or an encoded parametervalue calculated during encoding to output the bitstream. When entropyencoding is applied, the symbol is expressed by allocating a smallnumber of bits to a symbol having a high generation probability and alarge number of bits to a symbol having a low generation probability,and as a result, the size of a bitstream for symbols to be encoded maybe reduced. Accordingly, compression performance of video encoding maybe enhanced through the entropy encoding. The entropy encoding module150 may use encoding methods such as exponential-Golomb,context-adaptive variable length coding (CAVLC), and context-adaptivebinary arithmetic coding (CABAC) for the entropy encoding.

Since the picture encoding apparatus 100 according to the embodiment ofFIG. 1 performs inter prediction encoding, that is, inter-frameprediction encoding, a currently encoded picture needs to be decoded andstored to be used as the reference picture. Accordingly, the quantizedcoefficient is inversely quantized by the dequantization module 160 andinversely transformed by the inverse transform module 170. The inverselyquantized and inversely transformed coefficient is added to thepredicted block by the adder 175 and a reconstructed block is generated.

The reconstructed block passes though the filter module 180, and thefilter module 180 may apply at least one of a deblocking filter, asample adaptive offset (SAO), and an adaptive loop filter (ALF) to thereconstructed block or a reconstructed picture. The filter module 180may be called an adaptive in-loop filter. The deblocking filter mayremove block distortion which occurs on a boundary between blocks. TheSAO may add an appropriate offset value to a pixel value in order tocompensate for coding error. The ALF may perform filtering based on avalue acquired by comparing the reconstructed picture and the originalpicture. The reconstructed block which passes through the filter module180 may be stored in the decoded picture buffer 190.

FIG. 2 is a block diagram illustrating a configuration of a picturedecoding apparatus according to an embodiment of the present invention.

As described in detail in FIG. 1, the method or apparatus for scalablevideo encoding/decoding may be implemented by the extension of thegeneral picture encoding/decoding method or apparatus which does notprovide the scalability and the block diagram of FIG. 2 illustrates anembodiment of a picture decoding apparatus which may be a base of thescalable video decoding apparatus.

Referring to FIG. 2, a picture decoding apparatus 200 includes anentropy decoding module 210, a dequantization module 220, an inversetransform module 230, an intra prediction module 240, a motioncompensating module 250, an adder 255, a filter module 260, and adecoded picture buffer 270.

The picture decoding apparatus 200 may receive a bitstream output by anencoder and decodes the received bitstream in the intra mode or theinter mode, and output the restore picture, that is, the reconstructedpicture. In the intra mode, the switch may be shifted to ‘intra’, and inthe inter mode, the switch may be shifted to ‘inter’.

The picture decoding apparatus 200 may acquire a reconstructed residualblock from the received bitstream and generate a block reconstructed byadding the reconstructed residual block and the predicted block aftergenerating the predicted block, that is, the reconstructed block.

The entropy decoding module 210 entropy-decodes the input bit streamaccording to probability distribution to generate symbols including asymbol having a quantized coefficient form.

When entropy decoding is applied, the symbol is expressed by allocatinga small number of bits to a symbol having a high generation probabilityand a large number of bits to a symbol having a low generationprobability, and as a result, the size of a bitstream for each symbolmay be reduced.

A quantized coefficient is inversely quantized by the dequantizationmodule 220 and inversely transformed by the inverse transform module230, and the quantized coefficient is inversely quantized/inverselytransformed, and as a result, the reconstructed residual block may begenerated. In this case, the dequantization module 220 may apply aquantization matrix to the quantized coefficient.

In the intra mode, the intra prediction module 240 may generate theprediction block by performing a spatial prediction by using a pixelvalue of an already decoded block adjacent to a current block. In theinter mode, the motion compensation module 250 compensates for a motionby using a motion vector and a reference picture stored in the decodedpicture buffer 270 to generate the predicted block.

The residual block and the predicted block are added through the adder255 and the added blocks may pass through the filter module 260. Thefilter module 260 may apply at least one of the deblocking filter, theSAO, and the ALF to the reconstructed block or the reconstructedpicture. The filter module 260 may output the reconstructed picture,that is, the restore picture. The reconstructed picture is stored in thereference picture buffer 270 to be used in the inter prediction.

The constituent elements directly related to the video decoding amongthe entropy decoding module 210, the dequantization module 220, theinverse transform module 230, the intra prediction module 240, themotion compensation module 250, the filter module 260, and the decodedpicture buffer 270 included in the video decoding apparatus 200, forexample, the entropy decoding module 210, the dequantization module 220,the inverse transform module 230, the intra prediction module 240, themotion compensation module 250, the filter module 260, and the like aredistinguished from other constituent elements to be expressed by thedecoding unit.

Further, the video decoding apparatus 200 may further include a parsingunit (not illustrated) parsing information regarding the encoded videoincluded in the bit stream. The parsing unit may include the entropydecoding module 210, and may also be included in the entropy decodingmodule 210. The parsing unit may also be implemented as one constituentelement of the decoding unit.

FIG. 3 is a conceptual diagram schematically illustrating one example ofa scalable video coding structure using a plurality of layers accordingto the present invention. In FIG. 3, a group of picture (GOP) representsa picture group, that is, a group of pictures.

A transmission medium is required to transmit picture data andperformance thereof is different for each transmission medium accordingto various network environments. The scalable video coding method may beprovided to be applied to various transmission media or networkenvironments.

The video coding method (hereinafter, referred to as ‘scalable coding’or ‘scalable video coding’) supporting the scalability is a codingmethod that increases encoding and decoding performances by removinginter-layer redundancy by inter-layer texture information, motioninformation, a residual signal, and the like. The scalable video codingmethod may provide various scalabilities in spatial, temporal, quality,and view terms according to surrounding conditions such as transmissionbit rate, transmission error rate, a system resource, and the like.

Scalable video coding may be performed by using a multiple-layerstructure so as to provide a bitstream which is applicable to variousnetwork situations. For example, a scalable video coding structure mayinclude a base layer that compresses and processes the picture data byusing the general picture decoding method and may include an enhancementlayer that compresses and processes the picture data by using bothdecoding information of the base layer and the general decoding method.

Herein, a layer means a set of pictures and bitstreams that aredistinguished based on a spatial (for example, a picture size), atemporal (for example, a decoding order, a picture output order, andframe rate), quality, complexity, view, and the like.

A base layer may be referred to as a base layer or a lower layer. Anenhancement layer may be designated as an enhancement layer or a higherlayer. In this case, the lower layer may represent a layer that supportslower scalability than a specific layer and the higher layer mayrepresent a layer that supports higher scalability than a specificlayer. A layer which the specific layer refers to in encoding ordecoding may be referred to as a reference layer (alternatively,reference layer).

Referring to FIG. 3, for example, the base layer may be defined bystandard definition (SD), 15 Hz frame rate, and 1 Mbps bit rate, a firstenhancement layer may be defined by high definition (HD), 30 Hz framerate, and 3.9 Mbps bit rate, and a second enhancement layer may bedefined by 4K-ultra high definition (UHD), 60 Hz frame rate, and 27.2Mbps.

The format, frame rate, bit rate, and the like as one embodiment may bedecided differently as necessary. Further, the number of used layers isnot limited to the embodiment and may be decided differently accordingto a situation. For example, if a transmission bandwidth is 4 Mbps, datamay be transmitted at 15 Hz or less by decreasing the frame rate of theHD of the first enhancement layer.

The scalable video coding method may provide spatial, temporal, quality,and view scalabilities by the method described in the embodiment of FIG.3.

In this specification, the scalable video coding has the same as thescalable video encoding in terms of encoding and the scalable videodecoding in terms of decoding.

As described above, the scalability serves as a primary function of apresent video format due to heterogeneous communication networks andvarious terminals. The scalability information of the bitstream is veryimportant in order for all nodes to effectively and efficientlytransform the bitstream on a content delivery path. At present,important information associated with the bitstream in a high efficiencyvideo coding (HEVC) standard is described in a video parameter set(VPS). Further, it is very important to describe the importantinformation associated with the bitstream, for example, extractioninformation and scalability information even in a video standard thatextends the HEVC for providing the scalability.

Hereinafter, the present invention provides a method that efficientlyexpresses various scalability information of the bitstream encoded byusing the scalability video encoding and allows the bitstream extractorto extract a desired layer therethrough.

Representation of Bitstream Characteristics

A description for showing a characteristic of a scalable bitstream isdefined in the HEVC standard, and in the present invention,representation of the characteristic of the scalable bitstream intend tobe enhanced as below in order to apply to a scalable video codingstructure.

1) Time Window for Max. Bitrate Definition

Max. bitrate in the present scalable representation (representing areconstructed picture which is scalably decodable) represents an upperbound of bitrate within a time window for 1 sec.

However, peak bitrate or picture rate information in a timescale whichdepends on an application may be required. For example, a certainapplication may require only information within a time window of 30sec., whereas a certain application may require peak bitrate orlargest-burst information within a time window of 10 sec. Therefore, ascheme to represent at least one (one or more) time window is presentedas below for such a purpose.

Table 1 illustrates an embodiment of a syntax representing bitrateinformation within one or more time windows.

TABLE 1 Descrip- tor bit_rate_pic_rate_info( TempLevelLow, TempLevelHigh) {  num_max_bit_rate_windows_minus1 u(3)  for( j = 1; j <= num_max_bit_rate_windows_minus1; j++ ) max_bit_rate_calc_window[ j ]u(16)  num_max_pic_rate_windows_minus1 u(3)  for( j = 1; j <= num_max_pic_rate_windows_minus1; j++ ) max_pic_rate_calc_window[j ]u(16)  for( i = TempLevelLow; i <= TempLevelHigh; i++ ) { bit_rate_info_present_flag[ i ] u(1)  pic_rate_info_present_flag[ i ]u(1) if( bit_rate_info_present_flag[ i ] ) {  avg_bit_rate[ i ] u(16) for( j = 0; j <=  num_max_bit_rate_windows_minus1; j++ ) max_bit_rate [i ][ j ] u(16) } if( pic_rate_info_present_flag[ i ] ) { constant_pic_rate_idc[ i ] u(2)  avg_pic_rate[ i ] u(16)  for( j = 0; j<=  num_max_pic_rate_windows_minus1; j++ ) max_pic_rate [ i ][ j ] u(16)}  } }

Meanings of syntaxes illustrated in FIG. 1 are described below.

-   -   num_max_bit_rate_windows_minus1+1 represents the number of time        windows used to calculate the max. bitrate.    -   num_max_pic_rate_windows_minus1+1 represents the number of time        windows used to calculate the max, picture rate.    -   max_bit_rate_calc_window[j] represents the size of a j-th time        window used to calculate upper bounds for bitrate of        representations of sub-layers by the unit of 1/100 sec. A        default value of max_bit_rate_calc_window[0] is 100.    -   max_bit_rate_calc_window[j] represents the size of a j-th time        window used to calculate upper bounds for picture rate of        representations of sub-layers by the unit of 1/100 sec. A        default value of max_pic_rate_calc_window[0] is 25600.    -   A case in which bit_rate_info_present_flag[i] is “1” represents        that a description of the bit rate of the i-th sub-layer exists        and a case in which bit_rate_info_present_flag[i] is “0”        represents that the description of the bit rate of the i-th        sub-layer does not exist. A default value of        bit_rate_info_present_flag[i] is “1”.    -   A case in which pic_rate_info_present_flag[i] is “1” represents        that a description of the picture rate of the i-th sub-layer        exists and a case in which pic_rate_info_present_flag[i] is “0”        represents that the description of the picture rate of the i-th        sub-layer does not exist. A default value of        pic_rate_info_present_flag[i] is “1”.    -   avg_bit_rate[i] represents average bit rate of a representation        of the i-th sub-layer. avg_bit_rate[i] is similar as a content        described in an SVC standard.    -   max_pic_rate[i][j] represents an upper bound of the bitrate of        the representation of the i-th sub-layer as a value calculated        as described in the SVC standard by using the time window        represented by max_bit_rate_calc_window[j].    -   avg_pic_rate[i] represents average picture rate of the        representation of the i-th sub-layer (a picture unit for 256        sec.). avg_pic_rate[i] is similar as a content described in the        SVC standard.    -   max_pic_rate[i][j] represents an upper bound of the picture rate        of the representation of the i-th sub-layer as a value        calculated as described in the SVC standard by using the time        window represented by max_pic_rate_calc_window[j].

2) Bucket Size for Max. Bitrate Definition

Another method of describing bit rate information may use a leaky bucketmodel. The leaky bucket model is a mode to calculate respective bit ratevalues by using an amount of fixed data instead of a fixed timeinterval. An embodiment in a case using such a mode is illustrated inTable 2 below.

TABLE 2 Descrip- tor bit_rate_pic_rate_info( TempLevelLow, TempLevelHigh) {  num_max_bit_rate_values_minus1 u(3)  for( j = 1; j <= num_max_bit_rate_values_minus1; j++ ) max_bit_rate_calc_bucket_size[ j] u(16)  num_max_pic_rate_windows_minus1 u(3)  for( j = 1; j <= num_max_pic_rate_windows_minus1; j++ ) max_pic_rate_calc_window[ j ]u(16)  for( i = TempLevelLow; i <= TempLevelHigh; i++ ) { bit_rate_info_present_flag[ i ] u(1)  pic_rate_info_present_flag[ i ]u(1) if( bit_rate_info_present_flag[ i ] ) {  avg_bit_rate[ i ] u(16) for( j = 0; j <=  num_max_bit_rate_values_minus1; j++ ) max_bit_rate [i ][ j ] u(16) } if( pic_rate_info_present_flag[ i ] ) { constant_pic_rate_idc[ i ] u(2)  avg_pic_rate[ i ] u(16)  for( j = 0; j<=  num_max_pic_rate_windows_minus1; j++ ) max_pic_rate [ i ][ j ] u(16)}  } }

Meanings of syntaxes illustrated in FIG. 2 are described below.

-   -   num_max_bit_rate_values_minus1+1 means the number of max.        bitrates clarified in a corresponding syntax structure.    -   max_pic_rate_calc_bucket_size[j] clarifies the size of a j-th        leaky bucket used to calculate an upper bound of bit rate of the        representations of the sub-layers by the unit of kilobits.    -   num_max_pic_rate_windows_minus1 has a value of 0 when bitrate        information for the sub-layers is not defined.    -   max_pic_rate_calc_window[j] represents the size of a j-th time        window used to calculate upper bounds for bitrate of        representations of sub-layers by the unit of 1/100 sec. A        default value of max_pic_rate_calc_window[0] is 25600.    -   A case in which bit_rate_info_present_flag[i] is “1” represents        that a description of the bit rate of the i-th sub-layer exists        and a case in which bit_rate_info_present_flag[i] is “0”        represents that the description of the bit rate of the i-th        sub-layer does not exist. A default value of        bit_rate_info_present_flag[i] is “1”.    -   A case in which pic_rate_info_present_flag[i] is “1” represents        that a description of the picture rate of the i-th sub-layer        exists and a case in which pic_rate_info_present_flag[i] is “0”        represents that the description of the picture rate of the i-th        sub-layer does not exist. A default value of        pic_rate_info_present_flag[i] is “1”.    -   avg_bit_rate[i] represents average bit rate of a representation        of the i-th sub-layer. avg_bit_rate[i] is similar as a content        described in the SVC standard.    -   max_bit_rate[i][j] represents an upper bound of bit rate of the        representation of the i-th sub-layer. max_pic_rate[i][j]        represents an upper bound of the bitrate of the representation        of the i-th sub-layer as a value calculated as described in the        SVC standard by using the time window represented by        max_pic_rate_calc_bucket_size[j]. The max bitrate may be        calculated as below.

max_bit_rate[i][j]=max_bit_rate_calc_bucket_size[j]/SmallestInterval[i][j]

-   -   avg_pic_rate[i] represents average picture rate of the        representation of the i-th sub-layer (a picture unit for 256        sec.). avg_pic_rate[i] is similar as a content described in the        SVC standard.    -   max_pic_rate[i][j] represents an upper bound of the picture rate        of the representation of the i-th sub-layer as a value        calculated as described in the SVC standard by using the time        window represented by max_pic_rate_calc_window[j].

The syntaxes illustrated in Tables 1 and 2 above may be added toextension of a video parameter set (hereinafter, VPS) and defined in aform of a supplemental enhancement information (SEI) message.

Table 3 illustrates an embodiment of a syntax in which bitrateinformation is defined as the form of the SEI message.

TABLE 3 Descrip- tor layer_characteristics_info( payloadSize ) {  for( i= 0; i <= vps_max_layers_minus1 ; i++ ) { same_max_sub_layers_flag[ i ]u(1) if( !same_max_sub_layers_flag [ i ])  max_sub_layers_minus1[ i ]u(3) bit_rate_pic_rate_info( 0, (same_max_sub_layers_flag ?max_sub_layers_minus1 : vps_max_sub_layers_minus1) )   } }

In Table 3, same_max_sub_layers_flag[i] and max_sub_layers_minus1[i] mayhave the same meaning as a syntax having the same name to be describedbelow.

same_max_sub_layers_flag[i] may be information representing whether themaximum number of i-th sub-layers is equal to the maximum number of i-thsub-layers defined in a VPS.

max_sub_layers_minus1[i]+1 represents the number of sub-layers for i-thlayer.

3) Bitrate and Picture Rate Information for Different Temporal Periods

Present bitrate and picture rate information is described only in theVPS. However, encoded video signals may have different bitrate andpicture rate at different temporal periods. Therefore, the presentinvention proposes a technological scheme of the bitrate and the picturerate for the temporal period. Additional information proposed in Table 4below may be used to represent a partial characteristic of a videocontent. Whereas, the bitrate and the picture rate in the VPS are validonly for a fully encoded sequence.

For such a purpose, Table 4 illustrates a syntax that describes bitrateand frame rate for different temporal periods by using a new SEI message(e.g., “period_characteristics”).

TABLE 4 Descrip- tor period_characteristics( payloadSize ) {duration_flag u(1) if( duration_flag ) period_duration u(32)bit_rate_pic_rate_info( 0, vps_max_sub_layers_minus1 ) }

“period_characteristics” which is the SEI message newly defined in Table4 represents a characteristic of a temporal period of a video sequence,and the “period_characteristics” SEI message needs to be included in afirst access unit (AU) in a decoding order of a period to which thecorresponding SEI message is applied.

A meaning of the newly defined SEI message in Table 4 is describedbelow.

-   -   A case in which duration_flag is “0” means that a length of a        target temporal period is not described.    -   period_duration represents the length of the target temporal        period by the unit of a clock tick of a 90-KHz clock.

Layer Referencing

At present, a layer referencing method described in the HEVC isconfigured to describe all layers which a specific layer directly refersto. However, it may be apparent that in a specific dimension (s), orlayer, a specific layer (e.g., a quality layer “3”) directly refers to alower layer (e.g., a quality layer “2”) without a delay.

For such a purpose, the present invention proposes a scheme thatdescribes a dimension(s) having default direct dependency and describeslayer dependency separately in a description loop of a scalable layeronly for a dimension(s) that does not have the default indirectdependency.

Table 5 illustrates one example of a syntax in which a layer dependencyscheme is described in VPS_extension according to the present invention.

TABLE 5 Descrip- tor vps_extension( ) {  while( !byte_aligned( ) )vps_extension_byte_alignment_reserved_one_bit u(1)  avc_base_codec_flagu(1)  scalability_mask u(16)  for( i = 0; i <NumScalabilityTypes; i++ ){ dimension_id_len_minus1[ i ] u(3) default_dependency_flag [ i ] u(1) }  default_temp_dependency_flag u(1)  vps_nuh_layer_id_present_flagu(1)  // layer specific information  for( i = 1; i <=vps_max_layers_minus1; i++ ) { // mapping of layer ID to scalabilitydimension IDs if( vps_nuh_layer_id_present_flag )  layer_id_in_nuh[ i ]u(6) for( j = 0; j <= num_dimensions_minus1; j++ )−  dimension_id[i][j]u(v)  }  for( i = 1; i <= vps_max_layers_minus1 ; i++ ) {same_max_sub_layers_flag[ i ] u(1) if( same_max_sub_layers_flag [ i ]) profile_tier_level( 1,  vps_max_sub_layers_minus1 ) else { max_sub_layers_minus1[ i ] u(3)  profile_tier_level( 1, max_sub_layers_minus1[ i ] ) }  }  for( i = 1; i <=vps_max_layers_minus1; i++ ) { // layer dependencyspecific_dependency_flag [i] u(1) if( specific_dependency_flag [i] = =1){  num_direct_ref_layers[ i ] u(6)  for( j = 0; j <num_direct_ref_layers[ i ]; j++ ) { ref_layer_id[ i ][ j ] u(6)temporal_dim_description_flag[ i ][ j ] u(1) if(temporal_dim_description_flag[ i ][ j ] = =1) {  num_unref_temp_layers[i ][ j ] u(3)  for( k = 0; k <  num_unref_temp_layers[ i ][ j ]; k++ ) {unref_temp_layer_id[ i ][ j ][ k ] u(6) }  } }  } priority_description_flag  if( priority_description_flag ) {num_priority_policies_minus1 u(8) for(i = 0; i <num_priority_policies_minus1; i++)  priority_policy_description( )  } }

Syntax elements newly defined or modified in Table 5 have meaningsdescribed below.

-   -   A case in which default_dependency_flag[i] has “1” represents        that a scalability dimension or a scalability layer) i has        default dependency. This means that a layer in which        dimension_id[i]=n with a dimension or layer directly refers to a        layer dimension_id[i]=n−1. In the case of non-default        dependencies, the reference layer may be signaled by        specific_dependency_flag.    -   A case in which default_temp_dependency_flag has “1” represents        that a temporal dimension has the default dependency.    -   A case in which specific_dependency_flag[i] has “1” represents        that a reference (layer) relationship is to be described below.        A case in which specific_dependency_flag[i] has “0” represents        that the layer (dimension) I has the default dependency, has        indirect dependency, or has no dependency layer.    -   num_direct_ref_layers[i] specifies the number of layers which an        i-th layer directly refers to. The case represents that not        specified layers have the default dependency, has indirect        dependency, or has no dependency layer.    -   A case in which temporal_dim_description_flag[i][j] has “1”        means that a detailed dependency relationship regarding a        temporal sub layer of ref_layer_id[i][j] of the scalable layer.    -   num_unref_temp_layers[i][j] represents the number of temporal        sub layers which are not used as the dependency layer for a        scalable layer i.    -   unref_temp_layer_id[i][j][k] represents an id value of the        temporal sub layer which is not used as the dependency layer for        the scalable layer i.

Herein, that layer C directly refers to layer B means that a decoderneeds to use (non-decoded or decoded) data of layer B in order to decodelayer C. Moreover, when layer B directly uses data of layer A, layer Cdoes not directly refer to layer A.

The method proposed as above is difficult to represent differentdependency layer structures in respective temporal levels (that is, sublayers). Representing the dependency layer is required to achievedifferent dependency layer structures in the respective temporal levels.

Table 6 below illustrates one example of a syntax to describe thedependency layer to achieve different dependency layer structures in thetemporal levels. Each scalable layer is identified by layer_id andtemporal_id values.

TABLE 6 Descrip- tor vps_extension( ) { ..... for( i = 1; i <=vps_max_layers_minus1; i++ ) { for( t = 0; t <=max_sub_layers_minus1;t++) { // layer dependency num_direct_ref_scal_layers[ i ][ t ] u(9)for( j = 0; j < num_direct_ref_scal_layers[ i ][ t ]; j++ ) {ref_layer_id[ i ][ t ][ j ] u(6) ref_temporal_id[ i ][ t ][ j ] u(3) } }} }

Referring to Table 6, num_direct_ref_scal_layers[i][t] specifies thenumber of dependency layers that a present scalable layer (identified bylayer_id=I and temporal_id=t) directly refers to. Layers not specifiedherein may have the default dependency or an indirect dependency layer.

ref_layer_id[i][t][j] and ref_temporal_id[i][t][j] represent scalablelayers (layer_id=ref_layer_id[i][t][j] andtemporal_id=ref_layer_id[i][t][j]) which a present layer directly refersto.

When all layers (having unique layer ids) specified in all operationpoints defined in VPS of HEVC Version 1 have a direct or indirectdependency relationship each other, a content described bydirect_dependency_flag is included in the operation point, and as aresult, signaling by direct_dependency_flag may be omitted and theomission of the signaling may be known to layer_dependency_info_flag.

Table 7 illustrates one example of a syntax to representing a methodthat signals whether there is an interlayer dependency relationship inVPS extension according to the present invention.

TABLE 7 Descrip- tor vps_extension( ) { ..... layer_dependency_info_flagu(1) if (layer_dependency_info_flag)  for( i = 1; i <=vps_max_layers_minus1; i++ ) for( j = 0; j < i; j++ )direct_dependency_flag[ i ][ j ] u(1)

Referring to Table 7, a case in which layer_dependency_info_flag is 1represents that layer dependency associated information is described inVPS extension and a case in which layer_dependency_info_flag is 0represents that the layer dependency associated information is notdescribed in the VPS extension.

Further, a specific scalability dimension may be added to the defaulttype of the scalability dimension which is described at present. Thatis, as illustrated in Table 8, a priority ID that enables extracting andconsuming contents according to the order of a priority selected inencoding or after encoding and a region ID that enables extracting andviewing only a specific region may be added to the default type of thescalability dimension.

TABLE 8 Scalability scalability_mask dimension 0 none (base HEVC) 1spatial 2 quality 3 depth 4 multiview 5 priority ID 6 region ID 7 . . .15 reserved

Profile_Tier_Level (Representing Profile, Tier, and Level InformationRegarding Layer)

At present, profile_tier_level (profile, tier, and level information) isconfigured to be signaled as many as the number (that is,vps_max_sub_layers_minus1+1) of maximum sub-layers (alternatively,temporal sub-layers) in a bitstream for respective layers (layers havinglayer_id values) in an extension part of the VPS. However, therespective layers may have different numbers of sub-layers and it may bepreferable to describe the number of sub-layers in each layer for amiddle box. Therefore, signaling of profile_tier_level may be modifiedlike a part displayed by a shadow in a syntax of vps_extension( )described in Table 5 above, and meanings of modified syntax elements aredescribed as below.

Referring to Table 5, a case in which same_max_sub_layers_flag[i] is “1”represents that a max. sub-layer value of the temporal sub-layer of alayer i is vps_max_sub_layers_minus1+1.

max_sub_layers_minus1[i]+1 represents a max. sub-layer value of amaximum temporal sub-layer of the layer i.

same_max_sub_layers_flag[i] and max_sub_layers_minus1[i] may be signaledtogether with profile_tier_level as described in the embodiment of Table5 above and signaled separately as described in the embodiment of Table9 below.

TABLE 9 vps_extension( ) { ...............  for( IsIdx = 1; IsIdx <=vps_num_layer_sets_minus1;  IsIdx ++ ) { same_max_sub_layers_flag[IsIdx] u(1) if( !same_max_sub_layers_flag [IsIdx ]) max_sub_layers_minus1[IsIdx ] u(3) vps_profile_present_flag[ IsIdx ]u(1) if( !vps_profile_present_flag[ IsIdx ] ) profile_layer_set_ref_minus1[ IsIdx ] ue(v) profile_tier_level(vps_profile_present_flag[ IsIdx ], vps_max_sub_layers_minus1[IsIdx])  }

As described in detail, the maximum number of sub-layers (the maximumnumber of temporal sub-layers) is signaled for each layer to assist acapability negotiation or an extractor.

Further, in a case in which layers have different frame rates, and in acase in which max_one_active_ref_layer_flag is 1,NumDirectRefLayers[nuh_layer_id] is 1, or all_ref_layers_active_flag is1, the decoder may not distinguish two cases to be described below.

i) a case in which since an access unit (AU) is a picture which is notpresent in the bitstream (for example, due to the dependency layerhaving a different frame rate), the AU does not have a coded(encoded/decoded) picture for a dependency layer which a present layerdirectly refers to

ii) a case in which the coded (encoded/decoded) picture for thedependency layer which the present layer directly refers to is lostwhile being transmitted

The present invention proposes a method for distinguishing theaforementioned cases i) and ii). That is, in the present invention, itmay be judged whether a lower-layer picture for a higher sub-layer AU isintentionally missed or lost in the decoder or the middle box bysignaling the maximum number of sub-layers for each layer in the VPS.

In a method of describing the maximum value (number) of sub-layers foreach enhancement layer (that is, a layer of layer_id>0), there is ascheme that signals the maximum value of sub-layers of a correspondinglayer only for a layer having the maximum value of sub-layers other thanvps_max_sub_layers_minus1+1 signaled in the video parameter set (VPS) aspresented above or there may be schemes like an embodiment to bedescribed below.

A. A scheme that signals the maximum value of sub-layers of thecorresponding layer for each sequence parameter set (SPS) correspondingto each enhancement layer, that is, the layer of layer_id>0

Table 10 illustrates one example of a syntax representing a method ofsignaling the maximum value of sub-layers of the corresponding layer inthe SPS.

TABLE 10 seq_parameter_set_rbsp( ) { ...............sps_max_sub_layers_minus1 u(3) sps_temporal_id_nesting_flag u(1)............... }

B. A scheme that signals the number of sub-layers of each enhancement,that is, the layer of layer_id>0 in the video parameter set (VPS)extension

Table 11 illustrates one example of a syntax representing a method ofsignaling the maximum number of temporal sub-layers in the VPSextension.

TABLE 11 vps_extension( ) { ............... for( i = 1; i <=vps_max_layers_minus1; i ++ ) max_sub_layers_minus1[ i ] u(3)............... }

Referring to Table 11, max_sub_layers_minus1[i]+1 represents the maximumvalue of sub-layers (the maximum number of temporal sub-layers) havingan i-th layer.

C. A scheme that signals the maximum value of sub-layers in the SPS ofthe corresponding layer only when vps_max_sub_layers_minus1+1 signaledin the VPS and the maximum value of sub-layers of a specific layer aredifferent from each other

A general VPS syntax signals the maximum value of sub-layers in allbitstreams by using a value of vps_max_sub_layers_minus1 as illustratedin Table 12 below.

TABLE 12 Descrip- tor video_parameter_set_rbsp( ) {vps_video_parameter_set_id u(4) vps_reserved_three_2bits u(2)vps_max_layers_minus1 u(6) vps_max_sub_layers_minus1 u(3)vps_temporal_id_nesting_flag u(1) ............... }

In this case, when a layer is present, which has a maximum sub-layervalue which is not equal to a value of vps_max_sub_layers_minus1+1signaled in the VPS, the maximum sub-layer value may be signaled in theSPS of the enhancement layer as illustrated in Table 13.

TABLE 13 Descrip- tor seq_parameter_set_rbsp( ) { ............... if(nuh_layer_id ==0){ sps_max_sub_layers_minus1 u(3)sps_temporal_id_nesting_flag u(1)  } else { max_sub_layers_predict_flagu(1) if (!max_sub_layers_predict_flag) sps_max_sub_layers_minus1 u(3)  }............... }

Referring to Table 13, max_sub_layers_predict_flag is signaled when avalue of nuh_layer_id is larger than 0 (that is, in the case of theenhancement layer). When a value of max_sub_layers_predict_flag is 1,sps_max_sub_layers_minus1 may be inferred as vps_max_sub_layers_minus1and when the value of max_sub_layers_predict_flag is 0,sps_max_sub_layers_minus is explicitly signaled to the SPS.

When the maximum sub-layer value is signaled in the SPS corresponding tothe corresponding layer for each layer, maximum DPB size and maximumlatency time information signaled according to the maximum sub-layervalue may be signaled in the SPS. Alternatively, when the maximumsub-layer value is signaled in the VPS extension for each layer, valuesof sps_max_dec_pic_buffering_minus1, sps_max_num_reorder_pics, andsps_max_latency_increase_plus1 which are the maximum DPB size andmaximum latency time information signaled in the SPS may be signaled innot the SPS but the VPS extension, in order to remove parsing dependencybetween the VPS and the SPS.

A. In a scheme of signaling the maximum sub-layer value of thecorresponding layer for each sequence parameter set (SPS) correspondingto each enhancement layer, (that is, a layer of layer_id>0), the maximumDPB size and maximum latency time information may be signaled in the SPSas illustrated in Table 14.

TABLE 14 seq_parameter_set_rbsp( ) { ............... sps_max_sub_layers_minus1 u(3)  sps_temporal_id_nesting_flag u(1)...............  sps_sub_layer_ordering_info_present_flag u(1)  for( i =( sps_sub_layer_ordering_info_present_flag ?  0 :sps_max_sub_layers_minus1 );  i <= sps_max_sub_layers_minus1; i++ ) {sps_max_dec_pic_buffering_minus1[ i ] ue(v) sps_max_num_reorder_pics[ i] ue(v) sps_max_latency_increase_plus1[ i ] ue(v)  } ...............  }

B. In a scheme of independently signaling the maximum sub-layer value ofeach enhancement layer, that is, the layer of layer_id>0 in the videoparameter set (VPS) extension, the maximum DPB size and maximum latencytime information may be signaled in the VPS extension as illustrated inTables 15 and 16.

TABLE 15 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) {  max_sub_layers_minus1[i] u(3)sub_layer_ordering_info_present_flag[i] u(1) for( j = (sub_layer_ordering_info_present_flag[i] ? 0 : max_sub_layers_minus1[i]); j <= max_sub_layers_minus1[i]; i++ ) {  max_dec_pic_buffering_minus1[i ][ j ] ue(v)  max_num_reorder_pics[ i ][ j ] ue(v) max_latency_increase_plus1[ i ][ j ] ue(v) } } ...............  }

TABLE 16 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ )  max_sub_layers_minus1[i] u(3)...............  for( i = 1; i <= vps_max_layers_minus1; i ++ ){sub_layer_ordering_info_present_flag[i] u(1) for( j = (sub_layer_ordering_info_present_flag[i] ? 0 : max_sub_layers_minus1[i]); j <= max_sub_layers_minus1[i]; i++ ) {  max_dec_pic_buffering_minus1[i ][ j ] ue(v)  max_num_reorder_pics[ i ][ j ] ue(v) max_latency_increase_plus1[ i ][ j ] ue(v) } } ...............  }

C. In a scheme of signaling the maximum sub-layer value only when themaximum sub-layer value of each enhancement layer, that is, the layer oflayer_id>0 in the video parameter set (VPS) extension is different fromvps_max_sub_layers_minus1+1, the maximum DPB size and maximum latencytime information may be signaled in the VPS extension as illustrated insubsequent Examples C-1 to C-4.

Examples C-1 and C2 describe a scheme of signaling the maximum DPB sizeand maximum latency time information of all layers in the VPS extension.

Examples C-3 and C4 describe a scheme of signaling the maximum DPB sizeand maximum latency time information of the corresponding layer in theVPS extension only when the maximum sub-layer value and the value ofvps_max_sub_layers_minus1+1 are different from each other or the maximumsub-layer value and the value of vps_max_sub_layers_minus1+1 are equalto each other but the maximum DPB size and maximum latency timeinformation of all bitstreams signaled in the VPS are not equal to eachother.

Example C-1

TABLE 17 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3)sub_layer_ordering_info_present_flag[i] u(1) for( j = (sub_layer_ordering_info_present_flag[i] ? 0 : max_sub_layers_minus1[i]); j <= max_sub_layers_minus1[i]; i++ ) {  max_dec_pic_buffering_minus1[ i ][ j ] ue(v)   max_num_reorder_pics[ i][ j ] ue(v)   max_latency_increase_plus1[ i ][ j ] ue(v) } vps_profile_present_flag[ i ] u(1) if( !vps_profile_present_flag[ i ] ) profile_layer_set_ref_minus1[ i] ue(v) profile_tier_level(vps_profile_present_flag[ i ], vps_max_sub_layers_minus1[i])...............  } ...............

Example C-2

TABLE 18 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3)   }...............  for( i = 1; i <= vps_max_layers_minus1; i ++ ){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 : max_sub_layers_minus1[i]);  j <= max_sub_layers_minus1[i]; i++ ) { max_dec_pic_buffering_minus1[i ][ j ] ue(v) max_num_reorder_pics[ i ][ j ] ue(v)max_latency_increase_plus1[ i ][ j ] ue(v)  }   } ............... }

Example C-3

Table 19 illustrates signaling the maximum DPB size and maximum latencytime information in the VPS and Table 20 illustrates signaling themaximum DPB size and maximum latency time information in the VPSextension.

TABLE 19 video_parameter_set_rbsp( ) { ............... vps_max_layers_minus1 u(6)  vps_max_sub_layers_minus1 u(3)...............  vps_sub_layer_ordering_info_present_flag u(1)  for( i =( vps_sub_layer_ordering_info_present_flag ?  0 :vps_max_sub_layers_minus1 );  i <= vps_max_sub_layers_minus1; i++ ) { vps_max_dec_pic_buffering_minus1[ i ] ue(v)  vps_max_num_reorder_pics[i ] ue(v)  vps_max_latency_increase_plus1[ i ] ue(v)  } ...............}

TABLE 20 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3) else sub_layer_vps_buf_ordering_info_predict_flag[i] if(!same_max_sub_layers_flag[i] ∥!sub_layer_vps_buf_ordering_info_predict_flag[i]){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 : max_sub_layers_minus1i]);  j <= max_sub_layers_minus1[i]; i++) { max_dec_pic_buffering_minus1[i][ j ] ue(v) max_num_reorder_pics[ i ][ j ] ue(v)max_latency_increase_plus1[ i ][ j ] ue(v)  } } ...............  }

Referring to Table 20, sub_layer_vps_buf_ordering_info_predict_flag[i]represents whether maximum DPB size and maximum latency time informationof the i-th layer are the same as the maximum DPB size and maximumlatency time information of all of the bitstreams signaled in the VPSwhen the maximum sub-layer value of the i-th layer is equal tovps_max_sub_layers_minus1+1.

A case in which sub_layer_vps_buf_ordering_info_predict_flag[i] has “1”represents that the maximum DPB size and maximum latency timeinformation of the i-th layer are the same as the maximum DPB size andmaximum latency time information of all of the bitstreams signaled inthe VPS and a case in whichsub_layer_vps_buf_ordering_info_predict_flag[i] has “0” represents thatthe maximum DPB size and maximum latency time information of the i-thlayer are not the same as the maximum DPB size and maximum latency timeinformation of all of the bitstreams signaled in the VPS.

Maximum DPB size and maximum latency time information may be signaledonly when sub_layer_vps_buf_ordering_info_predict_flag[i] has “0” or themaximum sub-layer value is not equal to vps_max_sub_layers_minus1+1.When sub_layer_vps_buf_ordering_info_predict_flag[i] is not signaled,the value of sub_layer_vps_buf_ordering_info_predict_flag[i] is set to“0”.

Example C-3.1

Example C-3.1 differently expresses Example C-3 above and Table 21illustrates signaling the maximum DPB size and maximum latency timeinformation in the VPS and Table 22 illustrates signaling the maximumDPB size and maximum latency time information in the VPS extension.

TABLE 21 video_parameter_set_rbsp( ) {   ............... vps_max_layers_minus1 u(6)  vps_max_sub_layers_minus1 u(3)...............  vps_sub_layer_ordering_info_present_flag u(1)  for( i =( vps_sub_layer_ordering_info_present_flag ?  0 :vps_max_sub_layers_minus1 ); i <= vps_max_sub_layers_minus1; i++) {vps_max_dec_pic_buffering_minus1[ i ] ue(v) vps_max_num_reorder_pics[ i] ue(v) vps_max_latency_increase_plus1[ i ] ue(v)  } ............... }

TABLE 22 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3) else sub_layer_vps_buf_ordering_info_predict_flag[i] if(!sub_layer_vps_buf_ordering_info_predict_flag[i]){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 : max_sub_layers_minus1i]);  j <= max_sub_layers_minus1[i]; i++) {  max_dec_pic_buffering_minus1[i][ j ] ue(v)  max_num_reorder_pics[ i ][ j ] ue(v) max_latency_increase_plus1[ i ][ j ] ue(v)  } } ...............  }

Meanings of syntaxes added in Table 22 are the same as those of thesyntaxes having the same names. For example,sub_layer_vps_buf_ordering_info_predict_flag[i] is described withreference to Table 20.

Example C-4

TABLE 23 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3)   }...............  for( i = 1; i <= vps_max_layers_minus1; i ++ ){ if(same_max_sub_layers_flag[i]) sub_layer_vps_buf_ordering_info_predict_flag[i] u(1) if(!same_max_sub_layers_flag[i] ∥!sub_layer_vps_buf_ordering_info_predict_flag[i]){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 : max_sub_layers_minus1[i]);  j <= max_sub_layers_minus1[i]; i++ ) { max_dec_pic_buffering_minus1[i ][ j ] ue(v) max_num_reorder_pics[ i ][ j ] ue(v)max_latency_increase_plus1[ i ][ j ] ue(v)  }   }   } ............... }

Referring to Table 23, sub_layer_vps_buf_ordering_info_predict_flag[i]represents whether maximum DPB size and maximum latency time informationof the i-th layer are the same as the maximum DPB size and maximumlatency time information of all of the bitstreams signaled in the VPSwhen the maximum sub-layer value of the i-th layer is equal tovps_max_sub_layers_minus1+1.

A case in which sub_layer_vps_buf_ordering_info_predict_flag[i] has “1”represents that the maximum DPB size and maximum latency timeinformation of the i-th layer are the same as the maximum DPB size andmaximum latency time information of all of the bitstreams signaled inthe VPS and a case in whichsub_layer_vps_buf_ordering_info_predict_flag[i] has “0” represents thatthe maximum DPB size and maximum latency time information of the i-thlayer are not the same as the maximum DPB size and maximum latency timeinformation of all of the bitstreams signaled in the VPS.

Maximum DPB size and maximum latency time information of thecorresponding layer may be signaled only whensub_layer_vps_buf_ordering_info_predict_flag[i] has “0” or the maximumsub-layer value is not equal to vps_max_sub_layers_minus1+1. Whensub_layer_vps_buf_ordering_info_predict_flag[i] is not signaled, thevalue of sub_layer_vps_buf_ordering_info_predict_flag[i] is set to “0”.

Example C-4.1

Example C-4.1 differently expresses Example C-4 above.

TABLE 24 vps_extension( ) { ...............  for( i = 1; i <=vps_max_layers_minus1; i ++ ) { same_max_sub_layers_flag[i ] u(1) if(!same_max_sub_layers_flag [i ])  max_sub_layers_minus1[i ] u(3)   }...............  for( i = 1; i <= vps_max_layers_minus1; i ++ ){  if(same_max_sub_layers_flag[i])  sub_layer_vps_buf_ordering_info_predict_flag[i] u(1) if(!sub_layer_vps_buf_ordering_info_predict_flag[i]){  sub_layer_ordering_info_present_flag[i] u(1)   for( j = (sub_layer_ordering_info_present_flag[i] ?   0 : max_sub_layers_minus1[i]);  j <= max_sub_layers_minus1[i]; i++ ) { max_dec_pic_buffering_minus1[ i ][ j ] ue(v)  max_num_reorder_pics[ i][ j ] ue(v)  max_latency_increase_plus1[ i ][ j ] ue(v)   } }   }............... }

Meanings of syntaxes added in Table 24 are the same as those of thesyntaxes having the same names. For example,sub_layer_vps_buf_ordering_info_predict_flag[i] is described withreference to Table 23.

D. In a scheme of signaling the maximum number of sub-layers in the SPSof the corresponding layer only when vps_max_sub_layers_minus1+1signaled in the VPS and a maximum sub-layer value of a specific layerare different from each other, maximum DPB size and maximum latency timeinformation may be signaled in the SPS or the VPS extension as describedin Examples D-1 to D-3 below.

A general VPS syntax signals the maximum value of sub-layers in allbitstreams by using a value of vps_max_sub_layers_minus1 as illustratedin Table 25 below.

TABLE 25 Descrip- tor video_parameter_set_rbsp( ) {vps_video_parameter_set_id u(4) vps_reserved_three_2bits u(2)vps_max_layers_minus1 u(6) vps_max_sub_layers_minus1 u(3)vps_temporal_id_nesting_flag u(1) ............... vps_extension_flagu(1) if( vps_extension_flag ) { vps_extension( ) vps_extension2_flagu(1) if( vps_extension2_flag ) while( more_rbsp_data( ) )vps_extension_data_flag u(1) } rbsp_trailing_bits( ) }

In this case, in a case where the maximum sub-layer value is signaledwhen the maximum sub-layer value of the corresponding layer andvps_max_sub_layers_minus1+1 are not equal to each other in the SPS ofthe enhancement layer, an example in which the maximum DPB size andmaximum latency time information of the corresponding layer is signaledin the SPS will be described in Table 26 below.

Example D-1

TABLE 26 Descrip- tor seq_parameter_set_rbsp( ) { ...............  if(nuh_layer_id ==0){ sps_max_sub_layers_minus1 u(3)sps_temporal_id_nesting_flag u(1)  } else { max_sub_layers_predict_flagu(1) if (!max_sub_layers_predict_flag) sps_max_sub_layers_minus1 u(3)  }...............   if (nuh_layer_id ==0 ∥ (nuh_layer_id >0 &&  !max_sub_layers_predict_flag)){sps_sub_layer_ordering_info_present_flag u(1) for( i = (sps_sub_layer_ordering_info_present_flag ? 0 : sps_max_sub_layers_minus1); i <= sps_max_sub_layers_minus1; i+ ) { sps_max_dec_pic_buffering_minus1[ i ] ue(v)  sps_max_num_reorder_pics[i ] ue(v)  sps_max_latency_increase_plus1[ i ] ue(v) }   }............... }

Two examples below are examples in which maximum DPB size and maximumlatency time information of a layer having a maximum sub-layer valueequal to vps_max_sub_layers_minus1+1 among enhancement layers aresignaled.

Example D-2 is an example in which maximum DPB size and maximum latencytime information of all layers having the maximum sub-layer value equalto vps_max_sub_layers_minus1+1 are signaled.

Example D-3 describes a scheme of signaling maximum DPB size and maximumlatency time information of the corresponding layer in the VPS extensiononly when maximum DPB size and maximum latency time information inentire bitstreams are the same as the maximum DPB size and maximumlatency time information of the layer having the maximum sub-layer valueequal to vps_max_sub_layers_minus1+1 signaled in the VPS.

Example D-2

TABLE 27 Descrip- tor vps_extension( ) {  ............... for( i = 1; i<= vps_max_layers_minus1; i++ ){   max_sub_layers_vps_predict_flag[i]  if (max_sub_layers_vps_preidct_flag[i]){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 :vps_max_sub_layers_minus1);  j <= vps_max_sub_layers_minus1; i++ ) {max_dec_pic_buffering_minus1 [ i ][ j ] ue(v) max_num_reorder_pics[ i ][j ] ue(v) max_latency_increase_plus1[ i ][ j ] ue(v)  } } ............... }

Referring to Table 27, a case in whichmax_sub_layers_vps_predict_flag[i] has “1” represents that the maximum(temporal) sub-layer value of the i-th layer isvps_max_sub_layers_minus1+1 and a case in whichmax_sub_layers_vps_predict_flag[i] has “0” represents that the maximum(temporal) sub-layer value of the i-th layer has a value ofsps_max_sub_layers_minus1+1 signaled in the SPS (a SPS having the samenuh_layer_id value as the corresponding layer) of the correspondinglayer.

Maximum DPB size and latency time associated information of a layerhaving a maximum (temporal) sub-layer value equal tovps_max_sub_layers_minus1+1 is signaled in vps_extension and in a layerhaving a maximum (temporal) sub-layer value different fromvps_max_sub_layers_minus1+1 is signaled as described in Example D-1.

Example D-3

TABLE 28 Descrip- tor vps_extension( ) {  ............... for( i = 1; i<= vps_max_layers_minus1; i++ ){   max_sub_layers_vps_predict_flag[i]  if (max_sub_layers_vps_preidct_flag[i]){sub_layer_vps_buf_ordering_info_predict_flag[i] u(1)   if  (!sub_layer_vps_buf_ordering_info_predict_flag[i]){ sub_layer_ordering_info_present_flag[i] u(1)  for( j = (sub_layer_ordering_info_present_flag[i] ?  0 :vps_max_sub_layers_minus1);  j <= vps_max_sub_layers_minus1; i++ ) {max_dec_pic_buffering_minus1[ i ][ j ] ue(v) max_num_reorder_pics[ i ][j ] ue(v) max_latency_increase_plus1[ i ][ j ] ue(v)  }  } } ............... }

Referring to Table 28, a case in whichmax_sub_layers_vps_predict_flag[i] has “1” represents that the maximum(temporal) sub-layer value of the i-th layer isvps_max_sub_layers_minus1+1 and a case in whichmax_sub_layers_vps_predict_flag[i] has “0” represents that the maximum(temporal) sub-layer value of the i-th layer has a value ofsps_max_sub_layers_minus1+1 signaled in the SPS (a SPS having the samenuh_layer_id value as the corresponding layer) of the correspondinglayer.

sub_layer_vps_buf_ordering_info_predict_flag[i] represents whethermaximum DPB size and maximum latency time information of the i-th layerare the same as the maximum DPB size and maximum latency timeinformation of all of the bitstreams signaled in the VPS when themaximum sub-layer value is equal to vps_max_sub_layers_minus1+1.

A case in which sub_layer_vps_buf_ordering_info_predict_flag[i] has “1”represents that the maximum DPB size and maximum latency timeinformation of the i-th layer are the same as the maximum DPB size andmaximum latency time information of all of the bitstreams signaled inthe VPS and a case in whichsub_layer_vps_buf_ordering_info_predict_flag[i] has “0” represents thatthe maximum DPB size and maximum latency time information of the i-thlayer are not the same as the maximum DPB size and maximum latency timeinformation of all of the bitstreams signaled in the VPS. Only in a casein which sub_layer_vps_buf_ordering_info_predict_flag[i] has “0”, themaximum DPB size and maximum latency time information of thecorresponding is signaled.

In all of the cases, max_dec_pic_buffering_minus1[0][j],max_num_reorder_pics[0][j], and max_latency_increase_plus1[0][j] usevalues of sps_max_dec_pic_buffering_minus1[j], max_num_reorder_pics[j],and max_latency_increase_plus1[j] signaled in an SPS of a base layerhaving nuh_layer_id=0.

A DPB may be managed for each layer by using the aforementioned signaledDPB associated syntax information.

(1) In the case of a layer in which a decoded picture of a specificlayer is output by a decoder and displayed (that is, a layer in whichlayer_output_flag signaled in the VPS extension is ‘1’), a maximum DPBsize for the corresponding layer may be determined.

MaxDPBsize[i][j] represents a maximum DPB size when the i-th layerdecodes up to a temporal sub-layer in which temporal_id is j.

In a case in which a maximum (temporal) sub-layer value in allbitstreams to be decoded or a maximum (temporal) sub-layer value of alayer output to a display in the decoder is HighestTid, the maximum(temporal) sub-layer value of the i-th layer (in this case, i may be inthe range of 1<=i<=vps_max_layers_minus1) is A and in a case in whichA<HighestTid, a value of max_dec_pic_buffering_minus1[i][j] of thecorresponding layer may adopt a value ofmax_dec_pic_buffering_minus1[i][A] for A<j<=HighestTid. Similarly,max_num_reorder_pics[i][j] and max_latency_incresase_plus1[i][j] mayadopt values of max_num_reorder_pics[i][A] andmax_latency_increase_plus1[i][A] for A<j<=HighestTid.

Further, in a case in which an i-th layer (in this case, i may be in therange of 1<=i<=vps_max_layers_minus1) having a specific temporalsub-layer is used as a dependency layer of another layer (in a syntaxtable below, max_tid_il_ref_pics_plus1[i] represents that an i-th layerin which a value of temporal_id representing a temporal sub-layer isequal to or smaller than a value of max_tid_il_ref_pics_plus1[i]−1 isused as a dependency layer of another layer), a value ofMaxDPBsize[i][j] may adopt a value ofmax_dec_pic_buffering_minus1[i][max_tid_il_ref_pics_plus1[i]−1]+1 for jthat belongs to a range of max_tid_il_ref_pics_plus1[i]−1<j<=HighestTid.A value of MaxDPBsize[i][j] in the case of0<=j<=max_tid_il_ref_pics_plus1[i]−1 may adopt a value ofmax_dec_pic_buffering_minus1[i][j]+1.

Similarly, MaxReorderPics[i][j] and MaxLatencyIncreasePlus1[i][j] mayalso adopt values ofmax_num_reorder_pics[i][max_tid_il_ref_pics_plus1[i]−1] andmax_latency_increase_plus1[i][max_tid_il_ref_pics_plus1[i]−1], for jthat belongs to a range of max_tid_il_ref_pics_plus1−1[i]<j<=HighestTidand adopt values of max_num_reorder_pics[i][j] andmax_latency_increase_plus1[i][j] in the case of,0<=j<=max_tid_il_ref_pics_plus1[i]−1. Alternatively,MaxReorderPics[i][j] and MaxLatencyIncreasePlus1[i][j] in the case of0<=j<=HighestTid may also adopt values of max_num_reorder_pics [i][j]and max_latency_increase_plus1[i][j].

Table 29 illustrates one example of the VPS extension for managing theDPB for each layer by using the aforementioned syntax information.

TABLE 29 Descrip- tor vps_extension( ) { ... for( i = 1; i <=vps_max_layers_minus1; i++ ) for( j = 0; j < i; j++ )direct_dependency_flag[ i ][ j ] u(1) for( i = 0; i<vps_max_layers_minus1; i++ ) max_tid_il_ref_pics_plus1[ i ] u(3) ... }

(2) In the case of a layer in which a decoded picture of a specificlayer is not output by the decoder and displayed (that is, a layer inwhich layer_output_flag signaled in the VPS extension is ‘0’), a maximumDPB size for the corresponding layer may be determined.

In a case in which a maximum (temporal) sub-layer value in allbitstreams to be decoded or a maximum (temporal) sub-layer value of alayer output to a display in the decoder is HighestTid, the maximum(temporal) sub-layer value of the i-th layer (in this case, i may be inthe range of 1<=i<=vps_max_layers_minus1) is A and in a case in whichA<HighestTid, a value of max_dec_pic_buffering_minus1[i][j] of thecorresponding layer may adopt a value ofmax_dec_pic_buffering_minus1[i][A] for A<j<=HighestTid. Similarly,max_num_reorder_pics[i][j] and max_latency_incresase_plus1[i][j] mayadopt values of max_num_reorder_pics [i][A] andmax_latency_increase_plus1[i][A] for A<j<=HighestTid.

A value of MaxDPBsize[i][j] in the case of 0<=j<=HighestTid may adopt avalue of max_dec_pic_buffering_minus1[i][j]+1. MaxReorderPics[i][j] andMaxLatencyIncreasePlus1[i][j] in the case of 0<=j<=HighestTid may alsoadopt values of max_num_reorder_pics [i][j] andmax_latency_increase_plus1[i][j].

(3) Similarly as described above, but the maximum DPB size may also bemanaged as below.

MaxDecPicbuffering[i][j][k] represents a maximum DPB size when a valueof nuh_layer_id included in an i-th output layer set is j and a decodedmaximum temporal_id value is k.

The maximum DPB size may be decided as described in Table 30 by usingMaxDecPicbuffering[i][j][k].

TABLE 30 for(i=0; i<numOutputLayerSets; i++) {    IsIdx =output_layer_set_idx_minus1[i] + 1;  for (j=0;j<NumLayerInIdList[IsIdx]; j++) {    LayerId =LayerIdxInVps[LayerSetLayerIdList[IsIdx][j]];    if(output_layer_flag[IsIdx][j]) {      for(k=0;k<max_sub_layers_vps_minus1[LayerId]; k++)       MaxDexPicBuffering[i][LayerSetLayerIdList[IsIdx][j]][k]         =max_dec_pic_buffering_minus1[LayerId ][k]+1;       }else {     for(k=0;k<max_sub_layers_vps_minus1[LayerId]; k++)           if(k <max_tid_il_ref_pics_plus1[LayerId])           MaxDexPicBuffering[i][LayerSetLayerIdList[IsIdx][j]][k]           = max_dec_pic_buffering_minus1[LayerId][k]+1;            else        MaxDexPicBuffering[i][LayerSetLayerIdList[IsIdx][j]][k]         =max_dec_pic_buffering_minus1[LayerId][max_tid_il_ref_pics_plus1[LayerId]−1]+1;  }

Referring to Table 30, numOutputLayerSets represents the number ofoutput layer sets which the bitstream may support.

output_layer_set_idx_minus1[i]+1 represents an index value indicating alayer set corresponding to an i-th output layer set.

The layer set represents a set of layers included in a bitstreamgenerated through a sub-bitstream extraction process.

LayerSetLayerIdList[IsIdx][j] represents nuh_layer_id of a j-th layerincluded in an i-th layer set.

LayerIdxInVps[layer_id_in_nuh[i]] may be equal to i for0<=i<=vps_max_layers_minus1. In this case, layer_id_in_nuh[i] representsa value of nuh_layer_id signaled in a VCL NAL unit of an i-th layer.

max_sub_layers_vps_minus1[m] represents a value of temporal_id, that isa maximum temporal sub-layer of an m-th layer, −1.

max_tid_il_ref_pics_plus1[m] represents that a picture of m-th layer isused as the dependency picture only when the value of temporal_id isequal to or smaller than a value of max_tid_il_ref_pics_plus1[i]−1 amongm layers when an m-th layer is used as a dependency layer of an upperlayer.

Alternatively, the syntaxes may be signaled as described in Tables 31and 32 in order to manage parameters as described above.

TABLE 31 Descrip- tor vps_extension( ) { ... for( i = 1; i <NumOutputLayerSets ; i++ ) for( k = 0 ; k < NumLayersInIdList[output_layer_set_idx_minus1[ i ] + 1] − 1; k++ ) {sub_layer_vps_dpb_info_present_flag[ i ][ k ] u(1) for( j = (sub_layer_vps_dpb_info_present_flag[ i ] [ k ] ? 0 :vps_max_sub_layers_minus1; j <= vps_max_sub_layers_minus1; j++ ) {max_vps_dec_pic_buffering_minus1[ i ][ k ][ j ] ue(v) } } for( k = 0 ; k< vps_max_layers_minus1; k++ ) {sub_layer_vps_ordering_info_present_flag[ k ] u(1) for( j = (sub_layer_vps_ordering_info_present_flag[ k ] ? 0 :vps_max_sub_layers_minus1; j <= vps_max_sub_layers_minus1; j++ ) {max_vps_num_reorder_pics[ k ][ j ] ue(v) max_vps_latency_increase_plus1[k ][ j ] ue(v) } } ... }

TABLE 32 Descrip- tor vps_extension( ) { ... for( i = 1; i <NumOutputLayerSets ; i++ ) for( k = 0 ; k < NumLayersInIdList[output_layer_set_idx_minus1[ i ] + 1] − 1; k++ ) {sub_layer_vps_dpb_info_present_flag[ i ] [ k ] u(1) for( j = (sub_layer_vps_dpb_info_present_flag[ i ][ k ] ? 0 :max_sub_layers_minus1[LayerIdxInVps[LayerSetLayerIdList[IsIdx][j]]];;j<= max_sub_layers_minus1[LayerIdxInVps[LayerSetLayerIdList[IsIdx][j]]];j++ ) { max_vps_dec_pic_buffering_minus1[ i ][ k ][ j ] ue(v) } } for( k= 0 ; k < vps_max_layers_minus1; k++ ) {sub_layer_vps_ordering_info_present_flag[ k ] u(1) for( j = (sub_layer_vps_ordering_info_present_flag[ k ] ? 0 :max_sub_layers_minus1[k]; j <= max_sub_layers_minus1[k]; j++ ) {max_vps_num_reorder_pics[ k ][ j ] ue(v) max_vps_latency_increase_plus1[k ][ j ] ue(v) } } ... }

Representation of Priority Information

A method for representing a priority of a scalable layer of eachbitstream is proposed. As described above, the priority may be describedby a VPS or an SEI message (by, for example, layer_priority_info_messageas described below) and as one example, a priority for a layer may besignaled as described in Tables 33 and 34 below.

TABLE 33 Descrip- tor layer_priority_info( payloadSize ) { duration_flagu(1) if( duration_flag ) period_duration u(32)num_priority_policies_minus1 u(8) for(i = 0; i <num_priority_policies_minus1; i++) priority_policy_description( ) }

TABLE 34 Descrip- tor priority_policy_description( ) {  // mapping ofscalable layer to priority IDs  for( i = 0; i <= vps_max_layers_minus1;i++ ) for( j = 0; j <= vps_max_sub_layers_minus1; j++ )  priority_id[ i] [ j ] u(9)  //Priority Id Setting Uri  PriorityIdSettingUriIdx = 0  dopriority_id_setting_uri[ PriorityIdSettingUriIdx ]  while(priority_id_setting_uri[  PriorityIdSettingUriIdx++ ] != 0 ) }

Syntax elements newly defined or modified in Tables 33 and 34 havemeanings described below.

-   -   a case in which priority_description_flag is “1” represents        propriety information of the scalable layer is provided.    -   num_priority_policies_minus1+1 represents the number of priority        setting policies.    -   priority_id[i][j] represents a priority value of a layer in        which layer_id is i and temporal_id is j. priority_id[i][j]        represents that a value of the element is smaller, the priority        is higher.    -   priority_id_setting_uri[PriorityIdSettingUriIdx] represents a        universal resource identifier (URI) describing a method used to        calculate a priority_id value in a NAL unit header for a target        access unit set.

When a layer_priority_info message is present, the message needs to beincluded in a first access unit in terms of a decoding order of a cycleto which the message is applied.

FIG. 4 is a flowchart schematically illustrating a method for pictureencoding, which supports a scalable bitstream (hierarchical bitstream)according to an embodiment of the present invention. The method of FIG.4 may be performed by the picture encoding apparatus of FIG. 1.

Referring to FIG. 4, the encoding apparatus encodes scalabilityinformation of a bitstream (S400).

The scalability information of the bitstream represents informationrequired to efficiently code (encode/decode) a scalable characteristicof the bitstream in a video coding structure that supports a scalablebitstream (scalable layer).

For example, as described above, the scalability information of thebitstream may include characteristic information of the bitstream, layerdependency information on layers included in the bitstream, profile,tier, and level information on the layers included in the bitstream andpriority information on the layers included in the bitstream.

The characteristic information of the bitstream may include informationon bit rate or picture rate calculated by using a fixed time interval(e.g., a time window) or a fixed data amount (e.g., a bucket size) andinformation on bit rate or picture rate calculated by using a differenttime interval.

The layer dependency information may include dependency relationshipinformation (layer dependency information depending on whether to have adefault dependency relationship) on each layer included in the bitstreamand dependency relationship information on a temporal sub-layer.

The profile, tier, and level information represents information such asa profile, a tier, and a level for each layer included in the bitstreamand may be signaled as many as the maximum number of sub-layers of eachlayer.

The priority information may include priority information for each layerfor applying a priority policy to the layers included in the bitstream.The priority information may include, for example, priority IDinformation to extract and consume contents according to the priority orregion ID information to extract and view a specific region.

Further, the scalability information of the bitstream may includesub-layer information on the layers included in the bitstream. That is,the scalability information may include information on the maximumnumber of sub-layers which each layer may have. Further, the scalabilityinformation may include maximum DPB size and maximum latency timeinformation on each layer or each sub-layer.

The encoding apparatus may describe the scalability information of thebitstream through syntaxes including the VPS, the VPS extension, theSPS, the SEI message, and the like and encode the described syntaxinformation.

Herein, a method of describing the scalability information through thesyntaxes including the VPS, the VPS extension, the SPS, the SEI message,and the like has been described in detail with reference to Tables 1 to34, and as a result, a description thereof will be omitted in theembodiment.

The encoding apparatus transmits a bitstream including encodedscalability information (S410).

FIG. 5 is a flowchart schematically illustrating a method for picturedecoding, which supports a scalable bitstream (hierarchical bitstream)according to an embodiment of the present invention. The method of FIG.5 may be performed by a picture decoding apparatus of FIG. 2.

Referring to FIG. 5, the decoding apparatus receives a bitstreamincluding scalability information (S500).

The decoding apparatus decodes the received bitstream to acquire thescalability information on the bitstream (S510).

In this case, a process of acquiring the scalability information on thebitstream by decoding the bitstream may be regarded as an entropydecoding or parsing process and syntax element values of the scalabilityinformation may be output through the process.

The scalability information of the bitstream may include characteristicinformation of the bitstream, layer dependency information on layersincluded in the bitstream, profile, tier, and level information on thelayers included in the bitstream and priority information on the layersincluded in the bitstream, as described above.

The characteristic information of the bitstream may include informationon bit rate or picture rate calculated by using a fixed time interval(e.g., a time window) or a fixed data amount (e.g., a bucket size) andinformation on bit rate or picture rate calculated by using a differenttime interval.

The layer dependency information may include dependency relationshipinformation (layer dependency information depending on whether to have adefault dependency relationship) on each layer included in the bitstreamand dependency relationship information on a temporal sub-layer.

The profile, tier, and level information represents information such asa profile, a tier, and a level for each layer included in the bitstreamand may be signaled as many as the maximum number of sub-layers of eachlayer.

The priority information may include priority information for each layerfor applying a priority policy to the layers included in the bitstream.The priority information may include, for example, priority IDinformation to extract and consume contents according to the priority orregion ID information to extract and view a specific region.

Further, the scalability information of the bitstream may includesub-layer information on the layers included in the bitstream. That is,the scalability information may include information on the maximumnumber of sub-layers which each layer may have. Further, the scalabilityinformation may include maximum DPB size and maximum latency timeinformation on each layer or each sub-layer.

Meanwhile, the encoding apparatus may describe the scalabilityinformation of the bitstream through syntaxes including the VPS, the VPSextension, the SPS, the SEI message, and the like and encode and signalthe described syntax information as described above in detail.

Therefore, the decoding apparatus may acquire the scalabilityinformation on the bitstream by decoding the syntax elements includingthe VPS, the VPS extension, the SPS, the SEI message, and the like.

Herein, a method of describing the scalability information through thesyntaxes including the VPS, the VPS extension, the SPS, the SEI message,and the like has been described in detail with reference to Tables 1 to34, and as a result, a description thereof will be omitted in theembodiment.

FIG. 6 is a flowchart schematically illustrating a method for signalsub-layer information for a scalable layer in a pictureencoding/decoding structure, which supports a scalable bitstream(hierarchical bitstream) according to an embodiment of the presentinvention.

The method of FIG. 6 may be performed by the picture encoding apparatusof FIG. 1 or the picture decoding apparatus of FIG. 2. In FIG. 6, aprocess of signaling sub-layer information on the scalable layerperformed by the decoding apparatus is described for easy description.

Referring to FIG. 6, the decoding apparatus receives a bitstreamincluding a plurality of layers (S600).

In this case, the plurality of layers may include a base layer and atleast one enhancement layer.

The decoding apparatus acquires information on the maximum number ofsub-layers for the plurality of respective layers by decoding thereceived bitstream (S610).

The information on the maximum number of sub-layers is included in atleast one of video parameter set extension information, a videoparameter set, and a sequence parameter set to be signaled. The videoparameter set extension information may be a VPS extension syntax.

The method of signaling the information on the maximum number ofsub-layers by using the video parameter set extension information, thevideo parameter set, and the sequence parameter set has been describedin detail with reference to Tables 5, and Tables 9 to 13.

As one example, the decoding apparatus may be acquired from theinformation on the maximum number of sub-layers for each of theplurality of layers from the video parameter set extension information.In this case, the decoding apparatus acquires flag informationrepresenting whether the information on the maximum number of sub-layersis present in the video parameter set extension information to find themaximum number of sub-layers for each of the plurality of layers.

As another example, the decoding apparatus may acquire information onthe maximum number of sub-layers of a corresponding layer from the videoparameter set extension information for a layer in which the maximumnumber of sub-layers signaled in the video parameter set extensioninformation is different from the maximum number of sub-layers signaledin the video parameter set. In this case, the decoding apparatusacquires flag information representing whether the maximum number ofsub-layers signaled in the video parameter set extension information isequal to the maximum number of sub-layers signaled in the videoparameter set to determine the maximum number of sub-layers for thecorresponding layer.

As yet another example, the decoding apparatus may acquire theinformation on the maximum number of sub-layers for each of theplurality of layers from the sequence parameter set. That is, thedecoding apparatus may acquire information on the maximum number ofsub-layers of a corresponding layer from the sequence parameter setcorresponding to each of the base layer or the enhancement layer.

As yet another example, the decoding apparatus may acquire informationon the maximum number of sub-layers of a corresponding layer from thesequence parameter set when the maximum number of sub-layers signaled inthe video parameter set is not equal to the maximum number of sub-layerssignaled in the sequence parameter set of each of the plurality oflayers (base layer or enhancement layer). In this case, the decodingapparatus acquires flag information representing whether the maximumnumber of sub-layers signaled in the video parameter set is equal to themaximum number of sub-layers signaled in the sequence parameter set todetermine the maximum number of sub-layers for the corresponding layer.The flag information may be signaled in the case of the enhancementlayer.

For example, when the flag information represents that the maximumnumber of sub-layers signaled in the video parameter set is equal to themaximum number of sub-layers signaled in the sequence parameter set, themaximum number of sub-layers for the corresponding layer (enhancementlayer) may be decided as the maximum number of sub-layers signaled inthe video parameter set. On the contrary, when the flag informationrepresents that the maximum number of sub-layers signaled in the videoparameter set is not equal to the maximum number of sub-layers signaledin the sequence parameter set, the maximum number of sub-layers for thecorresponding layer (enhancement layer) may be decided as informationsignaled in the sequence parameter set.

Steps S600 to S610 described in detail may be performed by an entropydecoding unit, parsing unit or decoding unit of the decoding apparatus.

Further, when the method of signaling sub-layer information for thescalable layer is performed by the encoding apparatus in a pictureencoding/decoding structure that supports the scalable bitstream(hierarchical bitstream), the method may be performed in a procedureopposite to the procedure performed by the decoding apparatus.

For example, the encoding apparatus may decide and encode theinformation on the maximum number of sub-layers for each of theplurality of layers and transmit a bitstream including the encodedmaximum number of sub-layers. In this case, as described above, theinformation on the maximum number of sub-layers is stored in at leastone of the video parameter set extension information, the videoparameter set, and the sequence parameter set. The information on themaximum number of sub-layers is encoded by the entropy encoding unit orthe encoding unit of the encoding apparatus to be transmitted to thedecoding apparatus.

As described in the embodiment of the present invention, the informationon the maximum number of sub-layers is signaled for each layer toimprove performance and efficiency of a middle box and help performancenegotiation or a bitstream extracting process.

In the aforementioned embodiments, methods have been described based onflowcharts as a series of steps or blocks, but the methods are notlimited to the order of the steps of the present invention and any stepmay occur in a step or an order different from or simultaneously as theaforementioned step or order. Further, it can be appreciated by thoseskilled in the art that steps shown in the flowcharts are not exclusiveand other steps may be included or one or more steps do not influencethe scope of the present invention and may be deleted.

It will be appreciated that various embodiments of the present inventionhave been described herein for purposes of illustration, and thatvarious modifications, changes, substitutions may be made by thoseskilled in the art without departing from the scope and spirit of thepresent invention. Accordingly, the various embodiments disclosed hereinare not intended to limit the technical spirit but describe with thetrue scope and spirit being indicated by the following claims. The scopeof the present invention may be interpreted by the appended claims andthe technical spirit in the equivalent range are intended to be embracedby the invention.

1. A method for picture decoding supporting a plurality of layers, themethod comprising: receiving a bitstream including the plurality oflayers; and acquiring information on the maximum number of sub-layersfor each of the plurality of layers by decoding the bitstream.
 2. Themethod of claim 1, wherein the information on the maximum number ofsub-layers is included in video parameter set extension information tobe signaled.
 3. The method of claim 1, wherein the information on themaximum number of sub-layers for each of the plurality of layers isacquired in accordance with flag information representing whether theinformation on the maximum number of sub-layers is present.
 4. Themethod of claim 2, wherein: in the acquiring of the information on themaximum number of sub-layers for each of the plurality of layers, theinformation on the maximum number of sub-layers is acquired for a layerin which the maximum number of sub-layers signaled in the videoparameter extension information is different from the maximum number ofsub-layers signals in the video parameter set.
 5. The method of claim 4,wherein: in the acquiring of the information on the maximum number ofsub-layers for each of the plurality of layers, the information on themaximum number of sub-layers for each of the plurality of layers isacquired based on flag information representing whether the maximumnumber of sub-layers signaled in the video parameter extensioninformation is equal to the maximum number of sub-layers signals in thevideo parameter set.
 6. The method of claim 1, wherein: the plurality oflayers includes a base layer and at least one enhancement layer, and inthe acquiring of the information on the maximum number of sub-layers foreach of the plurality of layers, the information on the maximum numberof sub-layers for the enhancement layer in a sequence parameter setcorresponding to the enhancement layer is acquired.
 7. The method ofclaim 1, wherein: the plurality of layers includes a base layer and atleast one enhancement layer, and in the acquiring of the information onthe maximum number of sub-layers for each of the plurality of layers,the information on the maximum number of sub-layers for the enhancementlayer is acquired from the sequence parameter set when the maximumnumber of sub-layers signaled in the sequence parameter set is not equalto the maximum number of sub-layers signals in the video parameter set.8. The method of claim 7, wherein: the acquiring of the information onthe maximum number of sub-layers for each of the plurality of layersincludes acquiring flag information representing whether the maximumnumber of sub-layers signal in the sequence parameter set is equal tothe maximum number of sub-layers signaled in the video parameter set,when the flag information represents that the maximum number ofsub-layers signaled in the sequence parameter set is equal to themaximum number of sub-layers signaled in the video parameter set, theinformation on the maximum number of sub-layers for the enhancementlayer is determined as the maximum number of sub-layers signaled in thevideo parameter set, and when the flag information represents that themaximum number of sub-layers signaled in the sequence parameter set isnot equal to the maximum number of sub-layers signaled in the videoparameter set, the information on the maximum number of sub-layers forthe enhancement layer is decided as the maximum number of sub-layerssignaled in the sequence parameter set.
 9. A method for picture encodingsupporting a plurality of layers, the method comprising: acquiringinformation on the maximum number of sub-layers for each of theplurality of layers; and transmitting a bitstream including theinformation on the maximum number of sub-layers by encoding theinformation on the maximum number of sub-layers for each of theplurality of layers.
 10. The method of claim 9, wherein the informationon the maximum number of sub-layers is included in video parameter setextension information to be signaled.
 11. The method of claim 9, furthercomprising deciding flag information representing whether theinformation on the maximum number of sub-layers is present.
 12. Themethod of claim 10, wherein: in the acquiring of the information on themaximum number of sub-layers for each of the plurality of layers, theinformation on the maximum number of sub-layers is determined for alayer in which the maximum number of sub-layers signaled in the videoparameter extension information is different from the maximum number ofsub-layers signals in the video parameter set.
 13. The method of claim12, wherein: in the acquiring of the information on the maximum numberof sub-layers for each of the plurality of layers, flag informationrepresenting whether the maximum number of sub-layers signaled in thesequence parameter set is equal to the maximum number of sub-layerssignaled in the video parameter set is determined and encoded, and theinformation on the maximum number of sub-layers for each of theplurality of layers is determined based on the flag information.
 14. Themethod of claim 9, wherein: the plurality of layers includes a baselayer and at least one enhancement layer, and in the acquiring of theinformation on the maximum number of sub-layers for each of theplurality of layers, the information on the maximum number of sub-layersfor the enhancement layer is determined to be signaled through thesequence parameter set corresponding to the enhancement layer.
 15. Themethod of claim 9, wherein: the plurality of layers includes a baselayer and at least one enhancement layer, and in the acquiring of theinformation on the maximum number of sub-layers for each of theplurality of layers, the information on the maximum number of sub-layersfor the enhancement layer is determined to be signaled through thesequence parameter set when the maximum number of sub-layers signaled inthe sequence parameter set is not equal to the maximum number ofsub-layers signals in the video parameter set.
 16. The method of claim15, wherein: the acquiring of the information on the maximum number ofsub-layers for each of the plurality of layers includes determining andencoding flag information representing whether the maximum number ofsub-layers signaled in the sequence parameter set is equal to themaximum number of sub-layers signaled in the video parameter set, whenthe flag information represents that the maximum number of sub-layerssignaled in the sequence parameter set is equal to the maximum number ofsub-layers signaled in the video parameter set, the information on themaximum number of sub-layers for the enhancement layer is determined asthe maximum number of sub-layers signaled in the video parameter set,and when the flag information represents that the maximum number ofsub-layers signaled in the sequence parameter set is not equal to themaximum number of sub-layers signaled in the video parameter set, theinformation on the maximum number of sub-layers for the enhancementlayer is signaled through the sequence parameter set.
 17. An apparatusfor picture decoding supporting a plurality of layers, the apparatuscomprising a decoding module receiving a bitstream including theplurality of layers and decoding the bitstream to acquire information onthe maximum number of sub-layers for each of the plurality of layers.18. An apparatus for picture encoding supporting a plurality of layers,the apparatus comprising an encoding module determining information onthe maximum number of sub-layers for each of the plurality of layers andencoding the information on the maximum number of sub-layers for each ofthe plurality of layers to transmit a bitstream including theinformation on the maximum number of sub-layers.